Method for providing light to liquid crystal panel

ABSTRACT

The invention relates to a method of manufacturing a liquid crystal display, comprising forming a color filter array substrate including at least a red (R) color filter and a green (G) color filter; disposing a thin film transistor array substrate oppositely to the color filter array substrate; sealing a liquid crystal layer between the color filter array substrate and the thin film transistor array substrate; and disposing a backlight unit to a surface of the thin film transistor array substrate, said backlight unit providing white light having an adjusted blue spectrum using at least a light emitting diode (LED) unit.

This Application is a Divisional of U.S. patent application Ser. No.11/523,638 filed Sep. 20, 2006 now U.S. Pat. No. 7,656,476 for whichpriority is claimed under 35 U.S.C. §120 and which claims priority under35 U.S.C. §119(a) to Patent Application No. 10-2006-0044624 filed inKorea on May 18, 2006, the entire contents of each of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and moreparticularly, to a liquid crystal display and corresponding method usinga backlight unit that provides white light having an adjusted bluespectrum.

2. Description of the Background Art

A liquid crystal display includes a liquid crystal layer having adielectric anisotropy formed between upper and lower transparentinsulating substrates. Further, an electric field is applied to theliquid crystal layer to change the alignment of molecules of a liquidcrystal material such that the amount of light transmitted through theliquid crystal layer is adjusted, thereby displaying a desired image.

Because the liquid crystal display is small in size, is light in weight,and has low power consumption, various devices such as a computer and amobile telephone use liquid crystal displays.

Further, the liquid crystal display includes a color filter substrate, athin film transistor array substrate, and a liquid crystal panel havinga liquid crystal layer formed between the two substrates. The liquidcrystal display also includes a backlight unit for providing light tothe liquid crystal panel. The liquid crystal display may also include anexternal casing for protecting the liquid crystal panel and thebacklight unit.

Hereinafter, a liquid crystal display in the related art will bedescribed in detail.

As shown in FIG. 1, the related art liquid crystal display includesthree red (R), green (G) and blue (B) sub-pixels forming a unit pixel Pato provide a dot. Further, a plurality of dots is displayed on a frameto display a desired image.

As shown in FIG. 2, the unit pixel Pa includes a color filter 23 havingred (R), green (G), and blue (B) filters 23 a, 23 b and 23 c. The colorfilter array substrate also includes a transparent substrate 21 and ablack matrix 22 formed on the transparent substrate 21. The black matrix22 is for defining sub-pixel regions and blocking light leakage. Thecolor filter array substrate also includes an overcoat layer 24 forplanarizing the color filter layer 23.

Further, the black matrix layer 22 is formed on the transparentsubstrate 21 in a matrix shape and blocks light transmitted through thethin film transistor array substrate. Also, the color filter layer 23exhibits a desired color corresponding to a light signal transmittedthrough the thin film transistor array substrate. In addition, theovercoat layer 24 compensates a step difference of the color filterlayer 23 and protects the color filter layer 23.

As shown in FIG. 3, the light generated from a light source 30 (e.g.,fluorescent lamp) disposed on the rear surface of the liquid crystaldisplay is transmitted through a thin film transistor array substrate 10and the color filter layer 23 to emit red (R) light, green (G) light andblue (B) light. At this time, image information is displayed by mixingthe red (R), green (G) and blue (B) light. An example of a displayedimage is shown in FIG. 4.

As shown in FIG. 4, the displayed image has a relatively low definitionand brightness. That is, the light emitted from the backlight unit istransmitted through a first polarizer (not shown), an optical sheet (notshown), the thin film transistor array substrate 10, the liquid crystallayer, the color filter array substrate 20, and a second polarizer (notshown). Accordingly, the displayed image has a much lower definition andbrightness, compared to the light emitted from the backlight unit.

Further, due to the structure of the related art liquid crystal display,it is difficult to improve a contrast ratio and brightness of the image.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to address theabove-noted and other problems.

Another object of the present invention is to provide a liquid crystaldisplay and a method for providing light to a liquid crystal panel thatincreases a contrast ratio and brightness to improve the quality ofimage information.

Yet another object of the present invention is to simplify a method formanufacturing a color filter array substrate and reduce a manufacturingcost.

Still another object of the present invention is to compensate for thedeterioration of color and block light leakage by adjusting an opticalspectrum of a light emitting diode backlight unit emitting white light.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein, thepresent invention provides in one aspect a liquid crystal displayincluding a thin film transistor array substrate comprising sub-pixelregions, a color filter array substrate oppositely disposed to the thinfilm transistor array substrate, the color filter array substratecomprising color filters corresponding to at least a part of thesub-pixel regions, a liquid crystal layer formed between the colorfilter array substrate and the thin film transistor array substrate anda backlight unit configured to provide white light having an adjustedblue spectrum to a surface of the thin film transistor array substrateusing at least a light emitting diode (LED) unit.

According to another aspect, the present invention provides a method ofdriving a liquid crystal display. The method includes driving at least alight emitting diode (LED) unit in a backlight unit to provide whitelight to the liquid crystal display, determining a brightness of animage displayed on the liquid crystal display, and adjusting anintensity of a blue spectrum of the white light provided by thebacklight unit based on the determined brightness of the image.

According to another aspect, the present invention provides a method ofmanufacturing a liquid crystal display. The method includes forming acolor filter array substrate including at least a red (R) color filterand a green (G) color filter, disposing a thin film transistor arraysubstrate oppositely to the color filter substrate, sealing a liquidcrystal layer between the color filter array substrate and the thin filmtransistor array substrate, and disposing a backlight unit to a surfaceof the thin film transistor array substrate. Further, the backlight unitprovides white light having an adjusted blue spectrum using at least alight emitting diode (LED) unit.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by illustration only, since various changes and modificationswithin the spirit and scope of the invention will become apparent tothose skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawings,which are given by illustration only, and thus are not limitative of thepresent invention, and wherein:

FIG. 1 is an overview illustrating a unit pixel of a related art liquidcrystal display;

FIG. 2 is a cross-sectional view illustrating a color filter arraysubstrate of the related art liquid crystal display;

FIG. 3 is an overview explaining color exhibition of the liquid crystaldisplay in the related art;

FIG. 4 is a picture illustrating an image displayed by the structureshown in FIG. 3;

FIG. 5 is a perspective view illustrating a liquid crystal displayaccording to an embodiment of the present invention;

FIG. 6 is a cross-sectional view illustrating a color filter arraysubstrate of the liquid crystal display according to an embodiment ofthe present invention;

FIG. 7 is an overview illustrating a unit pixel of the color filterarray substrate according to an embodiment of the present invention;

FIGS. 8 to 10 are overviews illustrating various arrangement structuresof the unit pixel shown in FIG. 7;

FIG. 11 is a perspective view illustrating an LED backlight unit of theliquid crystal display according to an embodiment of the presentinvention;

FIG. 12 is a table explaining the property of the LED shown in FIG. 11;

FIG. 13 is an overview explaining a color exhibition of the liquidcrystal display according to an embodiment of the present invention;

FIG. 14 is a picture illustrating an image displayed by the structureshown in FIG. 13;

FIG. 15 is an overview illustrating a white LED unit of a backlight unitaccording to an embodiment of the present invention; and

FIG. 16 is a flowchart illustrating a method for providing light of abacklight unit according to an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

First, in one embodiment of the present invention, a white color filteris used instead of a blue color filter in a color filter substrate. Inaddition, the white color filter corresponds to a transparent colorfilter or no color filter such as a blank state material-less colorfilter, for example. The blank state material-less color filter meansthere is no material in an area corresponding to the color filter forthe white light. Rather, the area remains in a blank state.

Further, when white light including a blue spectrum having a highintensity is transmitted from a white LED unit of a backlight unit tothe white color filter, it is possible to exhibit a desired color. Thisis because human eyes can sense light in the visible light region (380to 760 nm). Green light having a wavelength of 555 nm is best sensed,but blue light has a relatively low sensitivity. Accordingly, it ispossible to exhibit a desired blue color using white light including theblue spectrum having a high intensity.

Turning first to FIG. 5, which is a perspective view illustrating aliquid crystal display according to an embodiment of the presentinvention. As shown, the liquid crystal display includes a color filterarray substrate 120, a thin film transistor array substrate 110, aliquid crystal panel having a liquid crystal layer 130 formedtherebetween, and a LED backlight unit 150 disposed on a rear surface ofthe liquid crystal panel.

In the liquid crystal panel, a plurality of gate lines 112 and aplurality of data lines 114 intersect each other on the thin filmtransistor array substrate 110. Further, sub-pixel regions P are definedby the intersection, and the defined sub-pixel regions P are formed in amatrix shape. A pixel electrode 118 is also formed in each sub-pixelregion P and a thin film transistor 116 is formed at the intersectionbetween each of the gate lines 112 and the data lines 114.

In addition, the thin film transistor 116 is a switching element andtransmits a data signal applied to the data line 114 to the pixelelectrode 118 in response to a gate signal of the gate line 112.Further, the pixel electrode 118 may be made of a transparent conductivematerial such as indium tin oxide (ITO) or indium zinc oxide (IZO) andgenerates an electrical field by switching the thin film transistor 116to adjust the alignment of the liquid crystal layer 130.

Also, in the liquid crystal layer 130, the alignment of liquid crystalmolecules varies depending on a vertical alignment between the thin filmtransistor array substrate 110 and the color filter array substrate 120or in-plane switching in the thin film transistor array substrate 110.Further, the amount of light transmitted depending on the alignment ofthe liquid crystal molecules varies to display various amount of imageinformation.

In addition, the liquid crystal layer 130 can operate in a twistednematic (TN) mode, a vertical alignment (VA) mode, an in-plane switching(IPS) mode or a fringe field switching (FFS) mode. Moreover, the colorfilter array substrate 120 faces the thin film transistor arraysubstrate 110 with the liquid crystal layer 130 interposed therebetweensuch that a uniform gap is maintained.

Next, as shown in FIG. 6, the color filter array substrate 120 includesa transparent substrate 121, a black matrix 122 formed on thetransparent substrate 121 in a matrix shape, and a color filter layer123 in which red (R), green (G), and white (W) color filters 123 a, 123b and 123 c are formed in the sub-pixel regions defined by the blackmatrix 122. An overcoat layer 124, which is a flat layer, may also beformed on the color filter layer 123. As discussed above, the white (W)color filter 123 c corresponds to a transparent color filter or blankstate material-less color filter. That is, wavelengths contained withinthe white light spectrum are allowed to pass through the white (W) colorfilter.

In addition, the black matrix 122 is formed at a position specified byan exposure process such that among light signals transmitted throughthe thin film transistor array substrate 110, light signals having ahigh distortion possibility are selectively blocked.

Further, the red (R), green (G) and white (W) color filters 123 a, 123 band 123 c are disposed in the respective sub-pixel regions defined bythe black matrix 122. As shown, ends of the color filters 123 a, 123 band 123 c or the boundary regions among the color filters 123 a, 123 band 123 c partially overlap the black matrix 122.

In addition, the red (R) color filter 123 a and the green (G) colorfilter 123 b are formed by applying a red and green color resin,respectively and performing an exposure and development process.Further, the red and green color filter 123 a, 123 b may be formed usingan inkjet printing method. The white (W) color filter 123 c is acolorless transparent filter made of a colorless transparent resin or isin a material-less blank state (i.e., no color filter).

Further, because the white (W) color filter 123 c transmits light thatwas transmitted through the substrate 110 and the liquid crystal layer130 from the rear surface without light loss, it is possible to increasethe brightness. In addition, when a material is not formed in the white(W) color filter 123 c, a manufacturing method can be simplified and amanufacturing cost can be reduced, because the step of forming the white(W) color filter 123 c is not performed.

Also, the overcoat layer 124 covers the color filter layer 123 such thatthe step difference of the color filter layer 123 is flat. The overcoatlayer 124 is made of a transparent resin material, for example.

In addition, when the white (W) color filter 123 c is made of atransparent resin, the white color filter 123 c and the overcoat layer124 may be formed in a single step using the same material. That is,after the red (R) and green (G) color filter 123 a, 123 b are formed,the white (W) color filter 123 c and the overcoat layer 124 may besimultaneously formed using the material of the overcoat layer 124.

Further, although the white (W) color filter 123 c may be made of atransparent resin material different from that of the overcoat layer 124or the same material as the overcoat layer 124, the filter 123 c andovercoat layer 124 may be formed by the same step or separate steps. Theovercoat layer 124 may also not be formed at all.

In addition, in the color filter layer 123, each of the color filters123 a, 123 b, and 123 c forms a sub-pixel. Thus, the red (R), green (G)and white (W) sub-pixels form a unit pixel Pb to display an image, asshown in FIG. 7.

That is, as shown in FIG. 8, a stripe arrangement structure includes thered (R), green (G) and white (W) sub-pixels sequentially arranged andthe sub-pixel of the same color is arranged in the same column. Inaddition, as shown in FIG. 9, a mosaic arrangement structure includesred (R), green (G) and white (W) sub-pixels sequentially arranged in arow and the sub-pixels of red (R), green (G) and white (W) are shiftedby one sub-pixel in a next lower row. Further, as shown in FIG. 10, adelta arrangement structure includes red (R), green (G) and white (W)sub-pixels arranged in a delta shape and the sub pixels of the samecolor are not adjacent to each other in all directions. However, thepresent invention is not limited to these arrangements.

Next, the structure of the LED backlight unit 150 according to anembodiment of the present invention will be described. In more detail,and as shown in FIG. 5, the LED backlight unit 150 is disposed on therear surface of the liquid crystal panel and provides light to theliquid crystal panel. As shown in FIG. 11, the LED backlight unit 150includes at least one white light emitting diode (LED) unit 151 foremitting white light as a light source, a reflective plate 152 forreflecting the white light emitted from the white LED unit 151, anoptical sheet 156 for diffusing and focusing the white light emittedfrom the white LED unit 151 and the reflective plate 152 and forproviding the white light to the liquid crystal panel (not shown). Thebacklight unit 150 also includes an outer casing 157, which is generallya bottom casing.

Further, the optical sheet 156 prevents a shape of the white LED unit151 from being displayed on a display surface of the liquid crystalpanel and provides the light having a uniform brightness distribution.To improve the diffusion of the white light generated at the white LEDunit 151, a diffusion sheet 153 and a prism sheet 154 may be provided. Aprotective sheet 155 may also be provided on the front surface of theprism sheet 154.

In addition, the reflective plate 152 is formed within the outer casting157 and has a plurality of holes formed in the surface thereof. Theholes correspond one-to-one to the positions of the white LED unit 151.Further, the white LED unit 151 is mounted on a lowest layer in theouter casing 157 in a predetermined pattern and is inserted in the holesof the reflective plate 152 to be exposed from the surface of thereflective plate 152. The optical sheet 156 is also disposed on thewhite LED unit 151.

Also, the white LED unit 151 includes chips for emitting red (R) light,green (G) light and blue (B) light. Further, white light is exhibited bymixing red (R), green (G) and blue (B) light. In addition, the chips arecontrolled by a LED driving unit such that the mixture of the red (R),green (G) and blue (B) light are well exhibited.

Also, as shown in FIG. 12, in an embodiment of the present invention,the white light emitted from the white LED unit 151 is formed by mixinga red (R) spectrum, a green (G) spectrum and a blue (B) spectrum havingdifferent wavelengths. The red spectrum has a wavelength of 645 to 700nm, the green spectrum has a wavelength of 490 to 530 nm, and the bluespectrum has a wavelength of 430 to 480 nm.

Thus, in an embodiment of the present invention, by increasing theintensity of the blue spectrum and using the white color filter insteadof the blue color filter the deterioration of the blue color or thereduction of the color index is compensated.

That is, in the image information displayed by the liquid crystaldisplay according to an embodiment of the present invention, because thecolor filter array substrate 120 having the white color filter is usedinstead of the blue color filter, the blue color index is reduced andthe yellow color is entirely displayed. Accordingly, when the white LEDunit 151 for emitting white light is used in the LED backlight unit 150and the blue component of the optical spectrum generated by the whiteLED unit 151 increases, it is possible to solve the reduction of theblue color index due to the use of the white (W) color filter.

In addition, the adjustment of the optical spectrum may be performedusing a dimming method for controlling the voltage applied to the whiteLED unit 151 and adjusting the light color depending on the amount ofcurrent for the applied voltage. Thus, the adjustment of the opticalspectrum is performed by adjusting the intensity of the optical spectruminstead of the wavelength of the optical spectrum (particularly, theblue spectrum). Thus, by increasing the intensity of the blue spectrum,that is, the current flowing through the blue LED in the white LED unitcorresponding to the brightness of the image to be displayed, thesubstantial white light includes the blue component.

The LED backlight unit 150 according to an embodiment of the presentinvention may also include an inverter (not shown) for controlling thevoltage applied to the white LED unit 151 and for increasing theintensity of the blue component among the red (R), the green (G) andblue (B) components forming the white light.

Thus, by increasing the intensity of the blue (B) spectrum among theoptical spectrum of the white LED unit 151 to include the blue color inthe white light, it is possible to compensate the deterioration of theblue light due to the removal of the blue (B) color filter. Further, byincreasing the light transmissivity using the white (W) color filter 123c, it is possible to increase the brightness and the contrast ratio (CR)of the liquid crystal display.

Turning next to FIG. 13, which is an overview for explaining a colorexhibition of an LCD according to an embodiment of the presentinvention. As shown, the light is transmitted from the white LED unit151 through the thin film transistor array substrate 110 and the colorfilter array substrate 120 including the overcoat layer 124, the red(R), green (G) and white (W) color filters 123 a, 123 b and 123 c, andthe transparent substrate 121.

At this time, the white LED unit 151 emits the white light and thecolorless white color filter 123 c emits the white light including theblue spectrum having a high intensity. Thus, as shown in FIG. 14, theimage displayed by the embodiment of the present invention has a higherdefinition and better color exhibition, compared to the image shown inFIG. 4 displayed using the blue color filter.

In the present invention, an LED for emitting white light is used. Forexample, combining three red, green and blue chips may be used to emitwhite light. The three chips are also separately controlled. In moredetail, FIG. 15 is an overview illustrating a white LED unit of thebacklight unit according to an embodiment of the present invention.

As shown in FIG. 15, the white LED unit 151 includes a red chip 151R, agreen chip 151G and a blue chip 151B. Further, the red chip 151R, thegreen chip 151G and the blue chip 151B are controlled by an LED drivingunit 210. Also, to increase the intensity of the blue spectrum of theblue chip 151B, the amount of current applied to the blue chip 151 isincreased. Thus, the white light including the blue spectrum having ahigh intensity can be obtained.

In another example, the backlight unit may include a plurality of LEDunits. Each unit comprises only one color of LED chip selected from red(R), green (G) and blue (B). Thus, the backlight unit may include a redLED unit, a green LED unit and a blue LED unit. The three LED units arealso separately controlled by an LED driving unit. That is, rather thana white LED unit combining the red (R) chip 151R, the green (G) chip151G and the blue (B) chip 151B as in the example of FIG. 15, aplurality of red, green and blue LED units may be separately used tocreate white light. One advantage of using separate red, green and blueLED units is that these LED units are less expensive than the white LEDunit 151 shown in FIG. 15, for example. Also, to increase the intensityof the blue spectrum of the blue LED unit, the amount of current appliedto the blue LED is increased. Thus, the white light including the bluespectrum having a high intensity can be obtained.

Next, FIG. 16 is a flowchart illustrating a method for providing thelight with a backlight unit according to an embodiment of the presentinvention. As shown, a controller determines if the LED unit in thebacklight unit is to be driven (S110). That is, the LED unit is drivenwhen the driving of the liquid crystal panel is driven.

Further, as discussed above, in case of a white LED unit, the LED unitincludes chips for emitting red (R) light, green (G) light and blue (B)light and emits white light by mixing the red (R), green (G) and blue(B) light. In addition, a current or voltage applied to the white LEDunit may be controlled by the LED driving unit 210 using a dimmingmethod which is to control the amount of voltage or current provided tothe LED unit.

Next, the brightness of a display image is confirmed (S120). Forexample, the brightness of the display image can be confirmed bychecking gradation data provided from an external system. Afterconfirming the brightness, the amount of current provided to the whiteLED unit is controlled to adjust the intensity of the blue spectrum(S130). Further, the white light including the blue spectrum having theadjusted intensity is provided to the liquid crystal panel (S140).

Subsequently, the white light is transmitted through the color filterarray substrate of the liquid crystal panel. More specifically, when thewhite light is transmitted through the white color filter, it ispossible to exhibit the blue color without alteration.

According to the liquid crystal display of the present invention, awhite (W) color filer is used in a color filter array substrate insteadof a blue (B) color filter such that the light is entirely transmittedthrough the white color filter. Accordingly, it is possible to increasethe light transmissivity and to improve the brightness and a contrastratio (C/R) of image information.

Further, the optical spectrum of a light emitting diode for emittingwhite light is controlled using a dimming method to increase theintensity of a blue spectrum. Accordingly, it is possible to compensatethe reduction of the blue color index due to the removal of the blue (B)color filter and to exhibit the image information with high definition.

In addition, because a separate step of forming the white (W) colorfilter is not performed, it is possible to simplify a manufacturingmethod and to reduce a manufacturing cost.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

1. A method of manufacturing a liquid crystal display comprising:forming a color filter array substrate, wherein the color filter arraysubstrate comprises a black matrix formed in a matrix shape to define ared sub-pixel region, a green sub-pixel region and a blue sub-pixelregion which form open regions of the black matrix, a red (R) colorfilter formed in the red sub-pixel region, a green (G) color filterformed in the green sub-pixel region, a white (W) color filter formed inthe blue sub-pixel region without forming a blue (B) color filter, andan overcoat layer covering the black matrix, the R color filter, the Gcolor filter and the W color filter, wherein the white color filter andthe overcoat layer are formed in a single process using a same materialafter the R color filter and the G color filter are formed; disposing athin film transistor array substrate oppositely to the color filterarray substrate; sealing a liquid crystal layer between the color filterarray substrate and the thin film transistor array substrate; anddisposing a backlight unit to a surface of the thin film transistorarray substrate, wherein the backlight unit comprises a light emittingdiode (LED) unit which provides white light having an adjusted bluespectrum to a surface of the color filter array substrate.
 2. The methodof claim 1, wherein the LED unit is a white (W) LED unit comprising acombination of a red LED chip, a green LED chip and a blue LED chip toproduce the white light, and wherein the white LED unit emits the whitelight by mixing red (R) light, green (G) light and blue (B) lightproduced by the red, green and blue chips, respectively.
 3. The methodof claim 1, wherein each LED unit comprises only one color of LED chipsselected from red (R), green (G) or blue (B).
 4. The method of claim 1,further comprising: arranging the red (R), green (G) and white (W) colorfilters in any one of a stripe structure, a delta structure, and amosaic structure.
 5. The method of claim 1, further comprising:providing an LED driving unit configured to adjust an intensity of theblue spectrum of the white light.